This invention relates to detection of explosives and in particular to the selective detection of very small amounts of vapors emanating from explosives.
Detection of explosives carried by persons or located in buildings, cars, or packages can be important to the protection of people and property. For example, it is essential that terrorists with bombs be intercepted prior to boarding commercial airplanes or entering buildings, and it is also desirable to be able to “sniff” buildings and vehicles to determine whether they contain explosives. To be effective, a detection system employed in screening persons for possible possession of explosives should be rapid, reliable have high selectivity and sensitivity, and be as non-intrusive as possible. In applications such as the searching of rooms or buildings or in screening vehicles other important characteristics of a detection system may include portability, ruggedness, and an ability to function in harsh environments.
Various techniques have been employed in detection of explosives. For example, nitric oxide-chemiluminescence technology has been used for analysis of explosive residues at the picogram level, but such systems included gas chromatographs or liquid chromatographs not useful in real time detection of explosives vapors. Electron capture detectors have been used commercially to detect dynamite, but have proven unable to achieve the high sensitivities (e.g. one part in 1014) needed for detection of certain explosives having very low vapor pressures. This limitation is due mainly to a lack of selectivity, i.e., the electron capture devices respond not only to explosives vapors, but also to substances such as oxygen, nitrogen oxides, halogenated solvents, water vapor, and phthalates which are present in excess amounts in the background. Dogs have been used effectively in certain circumstances but lack the sensitivity to consistently detect certain explosives such as RDX, PETN, and the water gels. Mass spectrometry and ion mobility spectroscopy have been shown to be highly sensitive to electronegative compounds including explosives; however, this high sensitivity has come at the expense of a loss of selectivity. If other electronegative species such as halogenated solvents, water vapors, and phthalates are present along with vapors of explosives, these species compete for detection and overload or reduce the effective sensitivity of mass spectrometers and ion mobility spectroscopes.
Accordingly, it is an object of the invention to provide an improved method and apparatus for detecting vapors from explosives.
It is an object of the invention to provide an explosives vapor detector capable of detecting explosives vapors essentially in real time at concentrations of as low as one part in 1014 or less.
It is an object of the invention to provide an explosives vapor detector which is highly sensitive to vapors of explosives but does not respond to substances which would interfere with detection of explosives.
It is an object of the invention to provide a highly sensitive, highly selective explosives vapor detector capable of achieving large sample preconcentrations without large pressure drops.
It is an object of the invention to provide systems incorporating a highly sensitive, highly selective explosives vapor detector which are capable of rapidly screening a succession of persons or articles for the presence of explosives.
It is an object of the invention to provide systems incorporating a highly sensitive, highly selective explosives vapor detector which may be used to screen vehicles or to search or monitor areas of buildings for the presence of explosives.
It is an object of the invention to provide a walk-through explosives vapor detection system which is rapid, effective, and of minimal intrusiveness to persons being screened.
It is an object of the invention to provide a microprocessor-controlled explosives vapor detection system whose sensitivity can readily be varied.